/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.tsfile.encoding.decoder;

import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
import org.apache.iotdb.tsfile.utils.BitReader;
import org.jtransforms.dct.DoubleDCT_1D;

import java.io.IOException;
import java.nio.ByteBuffer;

public class FreqDecoder extends Decoder {

    private double data[];

    private int readTotalCount = 0;

    private int nextReadIndex = 0;

    public FreqDecoder() {
        super(TSEncoding.FREQ);
    }

    @Override
    public double readDouble(ByteBuffer buffer) {
        if (nextReadIndex == readTotalCount) {
            loadBlock(buffer);
            nextReadIndex = 0;
        }
        return data[nextReadIndex++];
    }

    @Override
    public float readFloat(ByteBuffer buffer) {
        return (float) readDouble(buffer);
    }

    @Override
    public int readInt(ByteBuffer buffer) {
        return (int) Math.round(readDouble(buffer));
    }

    @Override
    public long readLong(ByteBuffer buffer) {
        return (long) Math.round(readDouble(buffer));
    }

    @Override
    public boolean hasNext(ByteBuffer buffer) throws IOException {
        return (nextReadIndex < readTotalCount) || buffer.hasRemaining();
    }

    @Override
    public void reset() {
        nextReadIndex = 0;
        readTotalCount = 0;
    }

    private void loadBlock(ByteBuffer buffer) {
        BitReader reader = new BitReader(buffer);
        // Block size with 16 bits
        this.readTotalCount = (int) reader.next(16);
        // Number of reserved components with 16 bits
        int m = (int) reader.next(16);
        // Exponent of quantification level with 16 bits
        int beta = (short) reader.next(16);
        // Decode index sequence
        int[] index = decodeIndex(m, reader);
        // Decode value sequence
        long[] value = decodeValue(m, reader);
        reader.skip();
        // Quantification
        double eps = Math.pow(2, beta);
        this.data = new double[readTotalCount];
        for (int i = 0; i < m; i++) {
            data[index[i]] = value[i] * eps;
        }
        DoubleDCT_1D dct = new DoubleDCT_1D(readTotalCount);
        dct.inverse(data, true);
    }

    private long[] decodeValue(int m, BitReader reader) {
        if (m == 0) {
            return new long[0];
        }
        // Decode the encoded bit width of the first value with 8 bits
        int bits = (int) reader.next(8);
        // Decode min{|v|}
        long min = reader.next(bits);
        // Decode all values
        long value[] = new long[m];
        int symbol;
        for (int i = 0; i < m; i++) {
            symbol = (int) reader.next(1);
            value[i] = reader.next(bits);
            bits = getValueWidth(value[i]);
            value[i] += min;
            if (symbol == 1) { // Negative value
                value[i] = -value[i];
            }
        }
        return value;
    }

    private int[] decodeIndex(int m, BitReader reader) {
        int[] value = new int[m];
        int bitsWidth = getValueWidth(getValueWidth(readTotalCount - 1));
        for (int i = 0; i < m; i += 8) {
            int bits = (int) reader.next(bitsWidth);
            for (int j = i; j < Math.min(i + 8, m); j++) {
                value[j] = (int) reader.next(bits);
            }
        }
        return value;
    }

    /**
     * Get the valid bit width of x
     *
     * @param x
     * @return valid bit width
     */
    private int getValueWidth(long x) {
        return 64 - Long.numberOfLeadingZeros(x);
    }
}
